Propagation delay in, or length of, an electrical line is typically measured by time domain reflectometry by providing an edge of a pulse to one end of a line (the other end of which is electrically open) by a driver, sensing when the edge has been applied to the line by sensing a first change in voltage at a detector connected to the same end of the line, and sensing the reflection back from the other end of the line by sensing a second change in voltage, the time between the two changes being twice the delay from the line. There are inaccuracies associated with detecting both changes in voltage, and in measuring such short nanosecond time intervals in general, and the results of numerous independent measurements are averaged to come up with a final measurement.